The proposed research program is an investigation of the relationship between form and function in macromolecular assemblies. Using the combined techniques of electron microscopy and X-ray diffraction, we propose to produce images of the multi-enzyme complexes, pyruvate dehydrogenase (PDC) and alpha-ketoglutarate dehydrogenase (KGDC), showing the arrangement of the component enzymes. The studies will use the techniques of reconstruction of three-dimensional images from electron micrographs, of protein crystallography and of X-ray scattering from solutions of the complexes. Knowledge of these structures is important to an understanding of the production of energy in the cell. Moreover, these structures exemplify aspects of macromolecular interaction important in subcellular organization. In addition, we are using the technique of three-dimensional image reconstruction from electron micrographs to investigate the structure of actin-containing structures found in non-muscle cells.